This invention relates to an improved apparatus and a method for connecting the conductors from a multi-wire cable to surface-mounted conductive pads on a printed wiring board. One of the key features of the present invention is that the cable conductors are directly connected to the printed wiring board conductors without the use of intermediate contacts or pins.
Flat cables which contain many separate conductors are commonly used in addressing the multiple connection needs. The prior art adopts two different types of flat cable. Flat conductors, rectangular in cross section, characterize one such type of cable. A common sleeve of insulation collectively insulates all the flat conductors contained in the cable by rigidly attaching each of the respective conductors to the inside of the sleeve in a spaced apart configuration so that they do not short against one another.
Round conductors characterize the other type of flat cable. Typically, individual tubes of insulation enclose each of the conductors. A plurality of such insulated round conductors are flexibly attached together to form a flat cable.
The currently available round conductor connectors are relatively expensive, multi-part devices. Typically, the conductor from a flat round conductor cable is connected to an intermediate contact which in turn is mated through a connector with another intermediate contact, which in turn is soldered to a printed wiring board trace.
The state of the art round conductor cable to intermediate contact connection typically involves an insulation displacement connector (IDC). The round conductor cable is pressed into an IDC connector header causing one end of the intermediate contact to puncture or displace the insulation and contact the cable conductors. The cable conductor thus makes an electrical connection to the internal intermediate contact.
The IDC connectors have problems in the areas of cost and reliability. These connectors tend to be expensive because they involve both a header and a multiplicity of intermediate contacts. The reliability of IDC connectors is low because the insulation puncturing contact to cable conductor connection is subject to two failure modes. In one failure mode, the puncturing contact cuts the cable conductor and an open circuit results. In the other failure mode, two adjacent intermediate contacts can short out.
Although relatively simple connectors presently exist to interface rectangular conductor flat cable to printed wiring board traces, such connectors are not satisfactory for round conductor cable. The reason for this is that the problems associated with making a suitable electrical termination with the rectangular conductor cable and round conductor cable are quite different. Thus, with rectangular conductor cable, insulation can be readily removed from only one side of the cable since the conductors will remain spaced apart because they are attached to the remaining insulation on the other side of the cable. However, for round conductor cables, the conductors, when exposed, are not rigidly attached to any insulation base. Thus, when insulation is removed from the round conductors, the uninsulated portions are free to move around and short with another conductor.